Adding a lean-to

Henro · Oct 7, 2003

Eastern Ohio...Western Pa...about the same thing...

When building my house I put 2x12 on 24" centers over the living room with a 16' span...

This year on my shed I put 2x8 on a 14 foot span on 24" centers... /forums/images/graemlins/blush.gif

I am sure both will be fine. BUT I don't need a load of snow in the living room in mid winter!

For a 16' span with the roof rafters at 24" on center, to be safe and comfortable I would go with 2x12s. The cost is not all that different...Actually quite small...

I doubt that there is much practical difference between a shallow slope and a 3 in 12 slope as far as snow shedding goes...the bigger concern is water getting back under the shingles and rotting the roofing sheeting, in my opinion.

If you get some of that rubberized material to put on the roof before you shingle it, when it is a shallow slope, you may be OK...

Remember that even if you are lower than you would like to be at the edge of the roof, because it is a slope, you will be gradually higher as you move away from the outside wall...

Just a couple additional thoughts... /forums/images/graemlins/smile.gif

PS...also there is a big difference in leakage between a roof over a heated space and an unheated space...with the unheated space being better since it does not melt the snow an the interface between the shingles and the snow...

cowboydoc · Oct 7, 2003

All I know is every building I have put up and the true 3 sided lean-to's I've built have all called for 2x12's in the plans. This last barn I put up I had 16' leans on the side of my barn 120' long and the plans called for double 2x12's or lvl's. I used double 2x12's because they were cheaper.

Henro · Oct 7, 2003

Just to add to what Cowboydoc is saying...

One 2x12 on 24" center is equal to two 2x12s on 48" centers...

As mentioned above, there are tables that tell you for a given snow load what you need. 2x12 on 24" centers, or 2x12 on 16" centers, etc.

It all depends on the snow load. Or better termed the live load. The total load the roof is supporting is the dead load[ plywood, shingles, roofing felt, etc] and the live load [ mostly snow, but includes you too if you are up there...].

I agree with what I think Cowboydoc is saying. It is cheap to add a little wood, especially when you are doing it yourself. Err on the conservative side...and be happy for the life of that roof!

Junkman · Oct 7, 2003

don't forget that the wider the span between rafters, the heavier that the plywood should be. If you use 2 x 8's and space them on 12" centers, you can get away with 1/2" plywood or chipboard. The cost will be about the same for the rafter lumber and you will have a better structure going 12" on center in my opinion... Junkman

EddieWalker · Oct 7, 2003

Why does the lower side have to be eight feet? I've seen plenty of side walls that are 6 feet tall that are never a problem. Even for people over 6 feet tall unless the access is through the side, which I don't see.

Lower the wall to six feet and increase you pitch.

Molerj · Oct 8, 2003

Thanks again. Some have missed that I will be using steel roofing. So the added weight of pywood, felt, & shingles will not be an issue. The only additional weight besides the steel will be the 1X4's or 2X4's that I run across the girders. Also when using steel the slope usually doesn't have to be that steep due to the fact of less resistance. Altho this is facing north & won't get the sun to melt the snow as fast. Deep snow is not the norm here in Eastern Ohio (70 miles west of Pittsburgh, Pa) altho we have gotten one or two large storms the last few years. But, I know it only takes one big wet snow to ruin my day! I think lowering the down side will be the best, as suggested. I would still like to keep at least 6 1/2 feet headspace on the lower side.

OkeeDon · Oct 8, 2003

My goal is to always keep the headers at least 80" in height. That's the standard height of a door; people are used to going through doors, and keeping it at that height tends to reduce surprises. Makes everyone using it feel more comfortable. It's only 2" more than the 6-1/2' you mentioned. My 6'4" tall son helped me to arrive at that; he would clear 6-1/2' by 2", but would feel uncomfortable. The rest of us height-challenged folks would probably not notice.

Soundguy · Oct 8, 2003

( Tell me exactly where you are located and I will run a snow drift calculation
)

First, my post specified that I was not taking into account regional weather.. i.e. snow loads. I made my statements based on my local.

As for the snow load.. don't worry.. I can run that in my head... as my kitchen freezer can probably hold all the snow that has fallen in central florida for the last decade.. etc.

( Send me a private email if you need more help.
)

Thanks, think I'll pass.. I already got the t-shirt.

Not trying to be obtuse here.. but the second thing to think about in engineering is cost vs risk ratio. ( first being safety and fit to purpose. ) -Anyone- can design a correct structure.. or overdesign it. But sometimes we just need to design for the 'job at hand'. We don't need to build a 10k$ roof over a water-well pump.. when all it needs is something decorative... etc.

(This is the exact reason why I specifically don't give long-distance engineering advice out. Only speculation and opinion. Hard to comment on something you havn't seen the site and plans & specifications for.)

Soundguy

Spencer · Oct 8, 2003

Soundguy, I think YooperDave's post was mostly directed at the original poster. Especially the two comments that you quoted.

Soundguy · Oct 8, 2003

Possibly so.

I actually agree with his advice, especially in that area, but see real problems with the owners specs ( what he wants them to be ) and what it will need to be.

In all actuality, the best advice we can give him is to contact a local architect/engineer, have them survey the site, draw up plans.. get a contractor.. pull the permits, get it built.
Absolute safest most correct way possible.

Soundguy